1. Field of the Invention
The present invention relates to a curing epoxy resin composition which permits water-repellent and ink-repellent surface treatment. Particularly, the present invention relates to an epoxy resin composition capable of forming a film pattern by ultraviolet irradiation and capable of forming a cured film which can be selectively removed by an excimer laser, a surface treatment method using the resin composition, a liquid-jet recording head subjected to ink-repellent treatment with the epoxy resin composition, and a liquid-jet recording apparatus using the liquid-jet recording head.
2. Description of the Related Art
In various fields, a method of applying a water-repellent coating to a member required to have water resistance and ink repellency to obtain these properties is generally known, and resin materials and coating materials used for the method have been developed. For example, films of fluoropolyolefin and a fluororesin coating material having perfluoro groups are thermally and chemically stable, excellent in weather resistance, water resistance, chemical resistance, solvent resistance, etc., and further excellent in release property, abrasion resistance and water repellency, and widely used for various applications.
Meanwhile, a liquid-jet recording head adapted to discharge liquid droplets such as ink droplets through discharge nozzles, causing the liquid droplets to adhere to a recording medium such as a sheet of paper so as to record or form an image thereon, is recently required to be able to discharge smaller liquid droplets, be driven with a higher driving frequency, and have a larger number of nozzles, in order to improve recording properties. Therefore, a treatment for maintaining the nozzle surface in a same surface state has becomes more important. However, it is difficult to selectively treat the surface of a nozzle or precisely treat the surface in the form of a pattern by using a known coating material so as to avoid ink adhesion. This is because firstly, a material mainly comprising a compound having a photosensitive functional group must be used as a surface treatment material for treating the surface in the form of a pattern so that the material has characteristics like a photoresist suitable for pattern treatment; but it is highly difficult to design the molecule of such a compound so that the compound has water repellency and ink repellency at the same time.
Secondly, if the nozzle surface can be treated with an existing fluorocarbon material, a film structure must be designed so as to maintain the properties of the surface for a long period of time. A material permitting such a pattern surface treatment having the above-described properties is greatly valuable for surface treatment of an ink-jet print head, as described below.
Namely, in an ink-jet recording system in which an ink is ejected as droplets, the discharge orifice (nozzle) is preferably designed to have the following characteristics:
(1) The residual ink of ink columns having turned into droplets is immediately held back into a nozzle.
(2) The ink droplets adhering to the nozzle surface can be readily wiped off by a cleaning operation.
(3) The nozzle surface has excellent scratch resistance against the cleaning operation and paper transfer.
(4) In repeated formation of droplets and ink refilling, a meniscus is formed on the nozzle surface (refer to reference numeral 23 in FIG. 1).
(5) The discharge direction is a normal to the meniscus.
(6) Even with an ink having low surface tension, or under low-negative pressure, the interfacial tension, i.e., the contact angle, is sufficient to form the meniscus.
The reason why the above characteristics are required for the discharge orifice is that, if a recording liquid such as an ink adheres to the periphery of the orifice, the discharge (flying) direction of the ink droplets discharged from the orifice is deviated, making it difficult to print highly accurately and degrading printing performance. In order to prevent adhesion of the ink to the vicinity of the discharge orifice, which causes a deviation in the discharge direction, methods have been developed in which a discharge orifice surface is subjected to a water-repellent treatment.
For example, Japanese Patent Laid-Open No. 2-39944 describes a method of ink-repellent treatment with a polymer having fluoroacetyl groups and silazane groups.
On the other hand, as a result of the increasing demand for sophisticated printers utilizing liquid-jet recording systems for recording images, the recording liquid to be used for such recording systems is also required to show sophisticated characteristics. More often, the recording liquid to be used for such recording systems is chemically regulated to be basic with a pH value of 7 to 11 in order to further improve dissolution stability and dispersion stability of contents, and thus a structural material highly resistant against alkali and hydrolysis has to be used for a printer member. Also, the miniaturization of liquid droplets discharged from the liquid-jet recording head requires that a water-repellent film formed on the liquid-jet recording head has fine processability. A conceivable method for finely processing a cured film of an epoxy resin is a method of removing the cured film of the epoxy resin by selective irradiation of an excimer laser. However, if the cured film itself has low abrasion property, it is difficult to finely process the cured film with precision. For example, when the cured film has insufficient abrasion property, a deposit is produced between a removed portion and a non-removed portion of the film.
In addition, when a recording liquid containing a polar organic solvent or a recording liquid showing such a high pH value is used, a water-repellent agent applied for treating the surface of the discharge orifice in order to satisfy the above requirements can damage the film forming property of the agent and the tight adhesion of the agent to the surface of the discharge orifice as it comes to contact with the solvent of the recording liquid, particularly the polar organic solvent of the recording liquid. Then, the coat of the water-repellent agent can peel off, resulting in a loss of surface water repellence.